注意:转换为ICO后效果不好.

源代码:

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

namespace paomiangege
{
    public class ImageConvert
    {
        private int ICON_W = 64;
        private int ICON_H = 64;

public ImageConvert()
        {
        }

//fileinpath,origaly picture file path,fileoutpath save filepath,index the ImageFormat you want to convert to
        public string Convert(string fileinpath, string fileoutpath, string index)
        {
            try
            {
                Bitmap bitmap = new Bitmap(fileinpath);
                index = index.ToLower();
                switch (index)
                {
                    case "jpg":  bitmap.Save(fileoutpath, ImageFormat.Jpeg); break;
                    case "jpeg": bitmap.Save(fileoutpath, ImageFormat.Jpeg); break;
                    case "bmp":  bitmap.Save(fileoutpath, ImageFormat.Bmp); break;
                    case "png": bitmap.Save(fileoutpath, ImageFormat.Png); break;
                    case "emf": bitmap.Save(fileoutpath, ImageFormat.Emf); break;
                    case "gif": bitmap.Save(fileoutpath, ImageFormat.Gif); break;
                    case "wmf": bitmap.Save(fileoutpath, ImageFormat.Wmf); break;
                    case "exif": bitmap.Save(fileoutpath, ImageFormat.Exif); break;
                    case "tiff":
                        {
                            Stream stream = File.Create(fileoutpath);
                            bitmap.Save(stream, ImageFormat.Tiff);
                            stream.Close();
                        } break;
                    case "ico":
                        {
                            Icon ico;
                            Stream stream = File.Create(fileoutpath);
                            ico = BitmapToIcon(bitmap, false);
                            ico.Save(stream);       //   save the icon
                            stream.Close();
                        }; break;
                    default: return "Error!";
                }
                return "Success!";
            }
            catch(Exception ex)
            {
                return ex.Message;
            }
        }

public string Convert(string fileinpath, string fileoutpath, string index,int width,int height)
        {
            if (width <= 0 || height <= 0)
                return "error!size illegal!";
            try
            {
                Bitmap mybitmap = new Bitmap(fileinpath);
                Bitmap bitmap = new Bitmap(mybitmap, width, height);
                index = index.ToLower();
                switch (index)
                {
                    case "jpg": bitmap.Save(fileoutpath, ImageFormat.Jpeg); break;
                    case "jpeg": bitmap.Save(fileoutpath, ImageFormat.Jpeg); break;
                    case "bmp": bitmap.Save(fileoutpath, ImageFormat.Bmp); break;
                    case "png": bitmap.Save(fileoutpath, ImageFormat.Png); break;
                    case "emf": bitmap.Save(fileoutpath, ImageFormat.Emf); break;
                    case "gif": bitmap.Save(fileoutpath, ImageFormat.Gif); break;
                    case "wmf": bitmap.Save(fileoutpath, ImageFormat.Wmf); break;
                    case "exif": bitmap.Save(fileoutpath, ImageFormat.Exif); break;
                    case "tiff":
                        {
                            Stream stream = File.Create(fileoutpath);
                            bitmap.Save(stream, ImageFormat.Tiff);
                            stream.Close();
                        } break;
                    case "ico":
                        {
                            if (height > 256 || width > 256)//ico maxsize 256*256
                                return "Error!Size illegal!";
                            Icon ico;
                            ICON_H = height;
                            ICON_W = width;
                            Stream stream = File.Create(fileoutpath);
                            ico = BitmapToIcon(mybitmap, true);
                            ico.Save(stream);       //   save the icon
                            stream.Close();
                        }; break;
                    default: return "Error!";
                }
                return "Success!";
            }
            catch (Exception ex)
            {
                return ex.Message;
            }
        }

private Icon BitmapToIcon(Bitmap obm, bool preserve)
        {
            Bitmap bm;
            // if not preserving aspect
            if (!preserve)        // if not preserving aspect
                bm = new Bitmap(obm, ICON_W, ICON_H);  //   rescale from original bitmap

// if preserving aspect drop excess significance in least significant direction
            else          // if preserving aspect
            {
                Rectangle rc = new Rectangle(0, 0, ICON_W, ICON_H);
                if (obm.Width >= obm.Height)   //   if width least significant
                {          //     rescale with width based on max icon height
                    bm = new Bitmap(obm, (ICON_H * obm.Width) / obm.Height, ICON_H);
                    rc.X = (bm.Width - ICON_W) / 2;  //     chop off excess width significance
                    if (rc.X < 0) rc.X = 0;
                }
                else         //   if height least significant
                {          //     rescale with height based on max icon width
                    bm = new Bitmap(obm, ICON_W, (ICON_W * obm.Height) / obm.Width);
                    rc.Y = (bm.Height - ICON_H) / 2; //     chop off excess height significance
                    if (rc.Y < 0) rc.Y = 0;
                }
                bm = bm.Clone(rc, bm.PixelFormat);  //   bitmap for icon rectangle
            }

// create icon from bitmap
            Icon icon = Icon.FromHandle(bm.GetHicon()); // create icon from bitmap
            bm.Dispose();        // dispose of bitmap
            return icon;        // return icon
        }
    }
}